From 247834f5299894de2ac0afeed3f48a944221afcf Mon Sep 17 00:00:00 2001
From: Brian Popow <popow@gmx.de>
Date: Sun, 15 Nov 2020 18:07:37 +0100
Subject: [PATCH 1/3] Use bulk conversion to rgba in Write8BitColor

---
 src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
index 454440f634..322d08e4c8 100644
--- a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
+++ b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
@@ -6,7 +6,6 @@
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Threading;
-using System.Threading.Tasks;
 using SixLabors.ImageSharp.Advanced;
 using SixLabors.ImageSharp.Common.Helpers;
 using SixLabors.ImageSharp.Memory;
@@ -340,15 +339,15 @@ private void Write8BitColor<TPixel>(Stream stream, ImageFrame<TPixel> image, Spa
         {
             using IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration);
             using IndexedImageFrame<TPixel> quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(image, image.Bounds());
+            using IMemoryOwner<Rgba32> rgbColorsBuffer = this.memoryAllocator.Allocate<Rgba32>(quantized.Palette.Length);
+            Span<Rgba32> rgbColors = rgbColorsBuffer.GetSpan();
 
             ReadOnlySpan<TPixel> quantizedColors = quantized.Palette.Span;
-            var color = default(Rgba32);
+            PixelOperations<TPixel>.Instance.ToRgba32(Configuration.Default, quantizedColors, rgbColors);
 
-            // TODO: Use bulk conversion here for better perf
             int idx = 0;
-            foreach (TPixel quantizedColor in quantizedColors)
+            foreach (Rgba32 color in rgbColors)
             {
-                quantizedColor.ToRgba32(ref color);
                 colorPalette[idx] = color.B;
                 colorPalette[idx + 1] = color.G;
                 colorPalette[idx + 2] = color.R;

From e4d0ffe6dbce456226c57af34e0b58c1374ad105 Mon Sep 17 00:00:00 2001
From: Brian Popow <popow@gmx.de>
Date: Sun, 15 Nov 2020 18:51:34 +0100
Subject: [PATCH 2/3] Dont use the default config in ToRgba32

---
 src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
index 322d08e4c8..c7e7a534b7 100644
--- a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
+++ b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
@@ -343,7 +343,7 @@ private void Write8BitColor<TPixel>(Stream stream, ImageFrame<TPixel> image, Spa
             Span<Rgba32> rgbColors = rgbColorsBuffer.GetSpan();
 
             ReadOnlySpan<TPixel> quantizedColors = quantized.Palette.Span;
-            PixelOperations<TPixel>.Instance.ToRgba32(Configuration.Default, quantizedColors, rgbColors);
+            PixelOperations<TPixel>.Instance.ToRgba32(this.configuration, quantizedColors, rgbColors);
 
             int idx = 0;
             foreach (Rgba32 color in rgbColors)

From 3970510861a6bf4cc4b7ecdafcffc69978f1df9c Mon Sep 17 00:00:00 2001
From: Brian Popow <popow@gmx.de>
Date: Sun, 15 Nov 2020 19:20:59 +0100
Subject: [PATCH 3/3] Use colorPalette span as destination of bulk conversion

---
 src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs | 17 ++++-------------
 1 file changed, 4 insertions(+), 13 deletions(-)

diff --git a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
index c7e7a534b7..01bdbd1c0b 100644
--- a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
+++ b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
@@ -339,22 +339,13 @@ private void Write8BitColor<TPixel>(Stream stream, ImageFrame<TPixel> image, Spa
         {
             using IQuantizer<TPixel> frameQuantizer = this.quantizer.CreatePixelSpecificQuantizer<TPixel>(this.configuration);
             using IndexedImageFrame<TPixel> quantized = frameQuantizer.BuildPaletteAndQuantizeFrame(image, image.Bounds());
-            using IMemoryOwner<Rgba32> rgbColorsBuffer = this.memoryAllocator.Allocate<Rgba32>(quantized.Palette.Length);
-            Span<Rgba32> rgbColors = rgbColorsBuffer.GetSpan();
 
             ReadOnlySpan<TPixel> quantizedColors = quantized.Palette.Span;
-            PixelOperations<TPixel>.Instance.ToRgba32(this.configuration, quantizedColors, rgbColors);
-
-            int idx = 0;
-            foreach (Rgba32 color in rgbColors)
+            PixelOperations<TPixel>.Instance.ToBgra32(this.configuration, quantizedColors, MemoryMarshal.Cast<byte, Bgra32>(colorPalette));
+            Span<uint> colorPaletteAsUInt = MemoryMarshal.Cast<byte, uint>(colorPalette);
+            for (int i = 0; i < colorPaletteAsUInt.Length; i++)
             {
-                colorPalette[idx] = color.B;
-                colorPalette[idx + 1] = color.G;
-                colorPalette[idx + 2] = color.R;
-
-                // Padding byte, always 0.
-                colorPalette[idx + 3] = 0;
-                idx += 4;
+                colorPaletteAsUInt[i] = colorPaletteAsUInt[i] & 0x00FFFFFF; // Padding byte, always 0.
             }
 
             stream.Write(colorPalette);